GB2129182A

GB2129182A - Method of driving matrix display device

Info

Publication number: GB2129182A
Application number: GB08325835A
Authority: GB
Inventors: Seigo Togashi
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1982-09-27
Filing date: 1983-09-27
Publication date: 1984-05-10
Also published as: DE3334933A1; FR2533730B1; JPS5957288A; DE3334933C2; JPH05714B2; HK31686A; GB8325835D0; GB2129182B; US4626841A; MY8600570A; FR2533730A1

Description

1 GB 2 129 182 A 1

SPECIFICATION Method of driving matrix display device

The present invention relates to a method of driving a matrix display device of the type in which each matrix element comprises a series connected combination of a non-linear element and a display element such as a liquid crystal display element. More specifically, the present invention relates to a drive method whereby non linear elements having a low value of threshold potential can be used, while maintaining a sufficiently large operating margin to allow for manufacturing deviations in element characteristics. Various types of matrix display devices, utilizing liquid crystal, electro-chromic or other types of display element, have now reached the stage of practical application, and methods are now being considered for producing high-density matrix displays. In general, the most satisfactory drive method which has been developed until now 85 for such displays has been the "active matrix" method, in which active elements (e.g. thin-film FET transistors) are employed to control the display elements, with one active element being provided for each display element and formed on a 90 display panel closely adjacent to the corresponding display element. This active matrix drive method is satisfactory from the aspect of providing a sufficiently high tolerance against the effects of stray deviations in the characteristics of 95 the display elements and the active elements themselves to ensure reliable operation. Such an active matrix display, utilizing transistors as control elements, has been described for example by B.J. Leichner et at in a report published in the 100 Proceedings of the IEEE, volume 59, No. 11, pages 1566 to 1579.

However it is desirable to simplify the configurations of all of the. elements of a matrix display as far as possible, in order to ensure maximum manufacturing yield, and to maximize the available display area as far as possible, both by minimizing the area occupied by the control elements and that occupied by connecting leads coupled to these control elements (e.g. the 110 connecting leads to the gate electrodes of transistors used as control elements). For this reason, it has been proposed to utilize a "active matrix" type of display, in which active elements, i.e. 2-terminal devices having a suitably non-linear 115 voltage/resistance characteristic, are used as control elements. Such a method has also been described by Leichner et at in the above reference. It has been proposed to use ceramic varistors as such non-linear control elements, for example as described by D.E. Castleberry in the IEEE ED-26, 1979, pages 1123 to 1128. In addition, it has been proposed to use MIM type diodes for such non-linear elements, for example as described by D.R. Baraff et at, in the IEEE ED-28, 1981, pages 736 to 739.

However, various problems have arisen with such prior art proposals for utilizing active elements.

These are: 1 - Lack of uniformity in element characteristics. 2. Operation of the display can be strongly affected by the distribution pattern of element characteristics, and by stray deviations in these characteristics. 3. The threshold potential Vth of the elements must be high. 4. The drive voltage levels required are high.

The most serious disadvantage of these prior art proposals has been that it is necessary to use active elements having a high level of threshold voltage, in spite of the fact that some types of display element such as liquid crystal display elements can operate at drive voltage levels as low as two or three volts. Elements having an inherently high value of threshold voltage, such as varistors or zener diodes, are not suited to formation on display matrix panels, e.g. in the form of thin-film elements closely adjacent to display elements, and in addition elements such as varistors have a considerable stray deviation in their threshold voltage values. In addition, it is desirable that such a matrix display device can be operated from a low value of supply voltage, to facilitate use in portable equipment, so that a requirement for high drive voltage levels is a significant disadvantage.

With the present invention, a new drive method is employed, whereby the disadvantages 2, 3 and 4 above are considerably reduced, and whereby it becomes possible to use elements which have a low value of threshold potential, so that disadvantage 4 is substantially eliminated. Thus, the method according to the present invention enables the threshold voltage (in the forward conduction direction) of a single PN diode to be utilized to control each display element, so that a suitable non-linear element can be configured as a pair of PN diodes connected in parallel with opposing polarities. Such diodes have a much higher degree of stability and uniformity of characteristics than the devices such as MIM diodes or varistors which have been previously proposed for use on non-linear elements in matrix display devices. In this way, the present invention considerably reduces problem 1 above, and brings such displays significantly closer to the stage of practical application.

According to the present invention, there is provided a method of driving a matrix display device formed of a plurality of row electrodes, a plurality of column electrodes and a plurality of matrix elements disposed at intersections of said row electrodes and column electrodes, each of said matrix elements comprising an electro-optical display element and a non-linear resistance element connected in series between one of said row electrodes and one of said column electrodes, said non-linear resistance element having a threshold voltage above which a significant increase in the resistance thereof occurs, said method comprising: applying row scanning signals successively to said row electrodes, said row scanning signals being applied periodically to 2 GB 2 129 182 A 2 corresponding ones of said row electrodes during successive scanning frame intervals, each of said row scanning signals being set to a first potential during a selection interval of fixed duration and timing within a frame interval and going to a second potential during a non-selection interval immediately thereafter and remaining fixed at said second potential during at least a major portion of the time which elapses until initiation of a succeeding selection interval during the succeeding frame interval, with the absolute value of said first potential being higher than the absolute value of said second potential and said first and second potentials having the same polarity; applying data signals varying in potential over a predetermined range to said column electrodes, with a synchronized relationship being established between said row scanning signals and said data signals such that a drive potential corresponding to a data value is applied across each of said matrix elements during a corresponding one of said selection intervals; the values of said first and second potentials of said row scanning signals and the potential range of said data signals being selected such that the absolute value of the difference between the drive potential established across a matrix element during a selection interval and the potential established across the display element of the matrix element during the immediately succeeding 95 non-selection interval is always less than or equal to the threshold potential of said non-linear resistance elements.

Fig. 1 is a diagram illustrating the basic configuration of a matrix display device; Fig. 2 is a diagram illustrating the basic configuration of a matrix display device utilizing non-linear resistance elements as passive control elements; Fig. 3 is a graph showing the general form of 105 the voltage-current characteristic of a non-linear resistance element for use in a matrix display device; Fig. 4 and Fig. 5 are respectively waveform diagrams illustrating drive signal waveforms of first and second prior art drive methods for a matrix display device;

Fig. 6 is a waveform diagram illustrating drive signal waveforms for an embodiment of a drive method for a matrix display device according to the present invention; Fig. 7, 8 and 9 are graphs for comparing optimum operating conditions of a prior art drive method and of the present invention, Fig. 10 is a circuit diagram illustrating a non- 120 linear resistance element used in an embodiment of the present invention; Fig. 11 and Fig. 12 are a plan view and cross sectional view respectively of a portion of an embodiment of the present invention, corresponding approximately to a single picture element. Fig. 13 shows the I-V characteristics of an amorphous silicon diode ring. 65 Fig. 14 is a diagram illustrating the distribution 130 of Vth.

Fig. 15 is a block diagram illustrating a matrix display device suitable for use with the method of the present invention.

Fig. 16 is a circuit diagram of a scanning signal drive circuit.

Fig. 17 is a timing chart for the circuit of Fig. 16.

Fig. 18 and Fig. 19 are circuit diagrams of embodiments of a controller circuit and a column electrode drive circuit respectively.

Fig. 20 shows an example of data signals for the case of an analog display device.

Fig. 21 is a circuit diagram of an embodiment of a circuit for automatically compensating for changes in Vth.

Before describing an embodiment of the present invention, a simple description will be given of a prior art display drive method. Fig. 1 is a diagram illustrating the general configuration of a matrix type of display device. In the diagram, S denotes a plurality of row electrodes, D denotes a plurality of column electrodes, with display elements C being disposed at positions corresponding to the intersections of these row electrodes and column electrodes. For convenience of description, it will be assumed in this specification that scanning signals are always applied to the row electrodes, to successively select rows of display elements such that the display elements within a selected row are either set into an activated state or left in a nonactivated state, in accordance with the states of data signals applied to the column electrodes during a selection interval. The complete set of rows is scanned during a time interval which will be referred to as a frame interval, and in general the state of activation or non-activation of each display element will be memorized by the element itself, i.e. as a charge stored in the inherent capacitance of the element or in an auxiliary capacitor coupled thereto.

Fig. 2 is a diagram for describing a matrix type of display device in which non-linear elements (i.e.

non-linear resistors) 2 are used to control the selection of the display elements during the corresponding selection intervals. Here, each of matrix elements M comprises a non-linear element L and display element C connected in series betwen a row electrode and column electrode at the intersection thereof. The voltage/current characteristic of an idealized nonlinear element is shown in simplified form in Fig. 3. As shown, the characteristic displays two different values of resistance Roff and Ron, at voltages above and below the threshold potential Vth.

Fig. 4 shows examples of drive signal waveforms for a prior art method of driving such a matrix display device. T1 and T2 denote two successive frame intervals, with all of the rows of the matrix being successively scanned during a frame interval by row scanning signals. This drive method is intended for use with liquid crystal display elements, and for this reason the polarity 3 GB 2 129 182 A 3 of the row scanning signal pulses are inverted in successive frame intervals, with the polarity of the data signals being correspondingly inverted. 0,, and 0,,,, are row scanning signal pulses which are successively applied to row electrodes S,, and Sn+1 respectively. During frame interval T1, signal 0,, goes to the selection potential Va during a selection interval tn, and remains at 0 potential at all other times. Similarly, signal 0,+, goes to selection potential Va during selection interval T,,+, within frame interval T1, and remains at the 0 potential at all other times. During frame interval r2, signal 0,, goes to the selection potential -Va during time interval tn, and is at the 0 potential at all other times, while similarly, signal 0n+1 goes to the selection potential -Va during time interval tln+l within frame interval T2, and is at the 0 potential at all other times.

Ym denotes a data signal which is applied to column electrode Dm. The potential of this signal varies between potentials Vc and -Vc, as shown in Fig. 4(a). During frame interval T1, Vc is -the activation potential of the data signal, (i.e. if the activated state, the following condition must be satisfied:

Vth > (Va + 2Vc) (1) A signal potential ((p.+, - 0), indicated by the full-line portions of Fig. 4(e), is applied to matrix element Mn+v, while the signal represented by the broken-line portions of Fig. 4(e) is applied to display element C,+,,,,. The hatchedline portions of Fig. 4(e) correspond to the OFF signal state. As stated in prior art reference 2 above, it is necessary for the following condition (which will be referred to hereinafter as condition W), to be satisfied:

(Va - V0 < Vth (2) However, as shown in Fig. 4(e), a single polarity of potential is maintained across the display element after it has been set in the non activated state, so that the operation will not be satisfactory for certain types of display element data signal applied to a column electrode is at that 85 such as liquid crystal display elements, which potential during a selection interval, then a sufficiently high potential will be established across the corresponding display element to activate it) and -Vc is the non- activation potential (i.e. if the data signal on a column electrode is at that potential during a selection interval, then the potential established across the corresponding display element will be sufficiently low that the corresponding display element will be left in the non- activated state). However during the immediately succeeding time interval T2, -Vc is the activation potential and Vc is the non activation potential, since the polarity of the row scanning signal is inverted in successive frame intervals.

Thus, a potential difference ((p, - 0J is applied to matrix element Mm,n i.e. the matrix element at the intersection of the nth row and the mth column, this potential being indicated by the full line portions in Fig. 4(d). The hatched-line portions in Fig. 4(d) indicate that the display element is held in the ON, i.e. activated state.

If a specific condition, designated as condition (1) below, is met, then the signal which is applied to the corresponding display element Cm,n will be as indicated by the broken-line portion in Fig. 4(d).

That is to say, the potential which is applied to that display element is heat at (Va + Vc - Vth) from (tn to tn'), which will be designated as the ON potential and will be assumed to be sufficiently high to hold that display element in the activated state, and is held at (-Va + Vc - Vth) during the time interval from tn' to the next selection interval.

In order to ensure that, for example, during frame interval TI the potential across the display element does not fall below the level indicated by the broken-line outline when the data signal goes to 120 -Vc, it will obviously be necessary that the threshold voltage Vth be equal to or greater than a potential (Va + Vc - Vth) + Vc. Thus, in order to ensure that this display element is held in the require a successively alternating bl-directional polarity drive signal. The condition for providing such an alternating drive signal can be expressed by replacing condition (2) above by the following condition (3):

Va - Vc Vth (3) In this case, of course, it will be necessary to ensure that the potential applied to a nonactivated display element (i.e. potential Va - Vc + Vth), referred to in the following as the nonactivation potential or Voff, will always be below the minimum potential which will activate a display element.

In the following, the first prior art drive method described above will be referred to as drive method A, while a modified version of that drive method which meets condition (3) above will- be referred to as drive method A.

Fig. 5 shows an example of drive signal waveforms for another prior art example which is described in prior art reference 2. In this case, the row scanning signals, e.g. 0',, and 0,,+,, vary between the two potentials Vs and 0, i.e. going to Vs during the selection intervals of the oddnumbered frame intervals, and going to OV in the selection intervals of the even-numbered frame intervals. The data signals, e.g. 01,, vary between potentials 2Vd, Vd, 0 and -Vd. During the oddnumbered frame intervals, the activation potential of the data signal is -Vd, and during the evennumbered frame intervals it is 2Vd.

As described in prior art reference 2, it is necessary for the following condition (4) to be met in order to ensure that a non-activated display element is held in the non-activated state:

Vd < Vth (4) If this condition is satisfied, then two problems 4 GB 2 129 182 A 4 will arise. Firstly, when a non-activation potential signal (for example 0,,+1 - 0%) is applied, then as indicated by numeral 14, a DC component will be introduced into the drive signal, i.e. AC symmetry is lost. Another severe problem is that a change in the potential across an activated display element, from (Vs + Vd - Vth) to (Vs - 2Vd - Vth), takes place at the timing indicated by numeral 12-, following a transition from frame interval T1 to frame interval T2 (or from frame interval T2 to T1) at the timing of the first activation pulse 12 of the next frame interval T2. The specific timing of this activation potential pulse depends upon the display states of other elements in that particular column, so that the time duration for which potential (Vs + Vd - Vth) is applied to a display element will also be dependent on the display states of other elements in the column. This will introduce cross-talk and lack of uniformity of operation. These two problems cannot be resolved by changing the operating conditions, such as has been described for prior art reference A.

As described in the above, various problems arise with both the bipolar drive methods described in prior art reference A and B. However, the problems which arise with regard to prior art reference A can be resolved to some extent by changing condition (2) given in prior art reference

A to condition (3), i.e. changing drive method A to drive method A.

In addition to conditions (2), (3) and (4) described above, the following quantities D, F and G are also important in evaluating a method of driving a matrix display device. These quantities 80 are as follows:

dVon dVth D = (-/ -) (5) Von Vth F = Vth/Von (6) G = Vp-p/Von (7) In the above, Von is the effective voltage which must be applied to produce activation of a display element. Vp-p is the peak-to-peak value of the drive signal voltage. A drive margin M will be defined, as:

M = VonNoff...... (8) Here, Voff is the effective voltage which must be applied to a display element to hold that display element in the OFF state, i.e. the erased or non-activated state. The values of Von and Vth will vary from the nominal values thereof, due to manufacturing deviations, and the amounts of such deviations are designated as dVon and dVth, respectively.

The larger the value of M, the better will be the degree of control of the display elements, and hence the better will be the display quality. With 110 drive method A,:

Von= Va + Vc - Vth (9) Voff = Va - Vc - Vth (10) The conditions for minimizing the values of D and F are established by changing condition (1) above to an equation, i.e. setting Vth = (Va + 2V0/2. The corresponding values of D, E and F for drive method A, D,, FA and C,, are given by the following equations:

FA = Vth/(Va + Vc - +Vth) (11) DA = FA/dVth (12) GA = 2Va/(Va + Va +Vc Vth) (13) By using the relationship Vth = (Va + 2Vc)/2, the following equations can be derived:

- 70 DA = (3M - 10 M (14) FA = (3M - W2M (15) GA = 4 (16) The above relationships are illustrated graphically in Fig. 7, 8 and 9, with curves 23, 25 and 27 therein respectively showing the variation of F, D and G with respect to drive margin M, for the improved prior art drive method A.

Fig. 6 shows the drive signal waveforms for a method of driving a matrix display device according to the present invention. Fig. 6(a) shows the row scanning signal 0% applied to matrix element M,,,.n, while Fig. 6(b) shows the row scanning signal 0%+1 applied to matrix element Mm,n+1. The row scanning signal 0% goes to a potential Va during a selection interval denoted as tn in frame interval T1, goes to a potential Vb during a succeeding non-selection interval portion tn,b of frame interval T1, remains at potential Vb during an initial non-selection interval portion tfn of the next frame interval T2, goes to a potential -Va during a selection interval t'n'of frame interval T2, and goes to a potential -Vb during a succeeding non-selection interval portion of frame interval T2. Prior to selection interval tn of frame interval T1, this signal is at potential -Vb, i.e. the waveforms shown in Fig. 6(a) are successively repeated. Similarly, row scanning signal 0n.., is at potential -Vb during an initial non-selection interval portion of frame interval T1, goes to potential Va during selection interval tn+i of frame interval T1, goes to potential Vb during a succeeding non-selection interval portion tl+llb Of frame interval T1, goes to potential -Va during selection interval t'n+l of the next frame interval T2, and goes to potential -Vb during the succeeding non-selection interval portion t'n+llb Of frame interval T2.

The data signal YM, shown in Fig. 6(c), varies between maximum and minimum potentials Vc and -Vc. In this embodiment, it is assumed that only ON and OFF display states are to be produced, however it is of course equally possible to utilize an analog type of continuously varying signal as data signal Y varying between the range Vc to -Vc, to provide an analog display.

The potential which is applied across matrix element M which is shown here as being held in the non-activated state, and across matrix element Min.n+l which is assumed to be in the activated, are shown in Fig. 6(e) and 6(d) respectively.

The voltage applied across an activated matrix element is indicated by the full-line portions of Fig.

6(d), while the resultant bias voltage appearing across the display element are indicated by the broken-line portions. The bias voltage across this display element following selection of the matrix element in frame interval T1, indicated by numeral 20, (i.e. the activation state holding voltage to which the display element is charged during selection interval t,,+,) is equal to (Va + Vc - Vth).

Similarly, the holding voltage applied across that display element after selection of the matrix element during frame interval T2, indicated by numeral 22, is equal to (-Va - Vc + Vth). It is an essential feature of the present invention that the difference between the maximum potential applied to a matrix element during a selection interval and the holding potential appearing across the display element during the succeeding non selection inteival is equal to or less than the value of threshold voltage Vth of the non-linear resistance element.

The voltage applied across a non-activated matrix element is shown by the full-line portions in Fig. 6(e), while the resultant bias voltage 100 appearing across the display element are indicated by the broken-line portions. The holding voltage produced in this case is equal to (Va - Vc Vth) during frame interval T1, and (-V - Vc + Vth) during frame interval T2.

It is a feature of this drive method that, rather than the row scanning signals going to a fixed potential during the pon-selection interval portions of a frame interval, (as in the examples of Fig. 4 and Fig. 5(d) and (e)), these signals remain at a fixed potential during a non-selection interval following a selection interval, this potential having the same polarity as that during the selection interval, and remaing at that potential until the next selection interval, whereupon an inversion of polarity takes place. For example, in the case of drive signal - 0,) the drive signal has a positive polarity during non-selection portion 17 of frame interval T1, and has a negative polarity during non-selection portion 18 of frame interval T2, with the corresponding bias potentials applied to the display element being designated by numerals 20 and 22.

The drive signal waveforms of this embodiment will now be described more specifically. The drive signals applied to the row electrodes are scanning signals which go to the,potential Va during odd numbered selection intrvals, go to a potential Vb during odd-numbered non-selection intervals, go to potential -Va during even-numbered selection GB 2 129 182 A 5 intervals, and go to potential -Vb during evennumbered non-selection intervals. The drive signals applied to the column electrodes are data signals, which have an absolute value of Vc or less.

It should be noted that although in the above, it is assumed that the row scanning signals remain at a fixed potential (e.g. Vb or -Vb) during the non-selection interval portion of a frame interval following a selection interval, it is only necessary that they remain at such a fixed potential during at least a major portion of the non- selection interval.

The drive signal waveforms of this embodiment of the present invention differ from the prior art with respect to the following points. Firstly, the scanning electrode signal p,, is a 3-valued signal, within each of frame intervals T1 and T2, as opposed to the prior art in which both (p,, and pr, are 2-valued signals. In the prior art examples discussed previously, all of the scanning signals 01 to 0,, 0, to 0', go to a common potential except during the selection intervals t, tn- In the case of prior art reference A, the common potential is zero. In the case of prior art reference B the common potential is 0 during T1 and is Vs during T2. Wit h embodiment C of the present invention, on the other hand, the drive signals take potentials Vb and -Vb, rather than a common potential, and the intervals during which these potentials are applied also vary in accordance with the scanning signals. Activation signals and non-activation signals are applied to the display elements of the present invention. For example in Fig. 6(d), a signal (On+i - 0) is applied to activate a display element, while a signal shown in the example of Fig. 6(e), i.e. signal (On - On) is applied to a nonactivated display element. The voltage which is applied across a display element during a selection interval will be equal to the maximum effective drive voltage applied during a frame interval (i.e. Va + Vc for an activated display element, and Va - Vc for a non-activated display element) minus the value of the threshold potential Vth.

The drive method according to the present invention will now be evaluated. As for (9) and 0 0) above, Von and Voff are given by the following equations:

Von= Va + Vc - Vth...... (17) Voff = Va - Ve - Vth (18) The condition for ensuring that an activated display element will be held in the activated state, corresponding to, condition (1) of the prior art methods, is given by the following:

Vth (Va - Vb + 2Vc) (19) Comparing equations (1) and (19), equation 19 enables Vb to be reduced by an amount equal to Vth. The values of quantities D, F and G defined hereinabove, for this embodiment of the present invention, will be designated as D,, F. and G,, and 6 GB 2 129 182 A 6 are given by the following:

D. = Vth/ (Va + Vc - Vth) 20 Fc = Vth/Wa + Vc - Vth) 21 Gc = 2Va/ (Va + Ve - Vth) (22) Each of these quantities can thus take a smaller value than is possible with the prior art examples.

The optimum operating conditions with the present invention are obtainedby equating both sides of relationship 19, that is by making:

Vth -. (Va - Vb + 2V0/2 (23) 60 In addition, although it is not essential condition, it is desirable that the potential during the time interval 15 in Fig. 6(e), i.e. the potential (Va - Vc), be greater than the potential during 15 time interval 16 in Fig. 6(e), i.e. the potential (Vb + Ve), in order to ensure reliable establishment of the activation potential condition. That is:

Va - Vb 2Vc (24) Combining equations 19 and 24 above, the following can be obtained:

Vth t Va- Vb t 2Vc (25) If the above relationships are interpreted as equations, then the quantities can be expressed as functions of the drive margin M, as follows: 80 Dc = (M - 1)/M (26) Fe = (M - 1)/M (27) G, = (3M - 1)/M (28) The relationships between the values of Va, Vb and Vc and the drive margin M, for optimum operation, are given by the following equations (29), (30) and 3 1:

Va:5 1Q M - 1 0M - 1) I.Vth/2 (29 Vb:5 ((M + 10M - 1)1Nth/2 (30 Vc:fVth/2 (31) It is also necessary to allow a certain tolerance in the threshold voltage Vth, which will be designated as AVth to provide for manufacturing deviations in the value of Vth of the display elements, and the effects of incident light acting on the display elements, etc. This amount of this tolerance can be determined as follows:

Va - Vb = Rth - AVth) Vc = Rth - AVtW/2 The relationships between the quantities F, D 110 and G (described hereinabove) and the drive Margin M for this embodiment, for the case of optimum operating conditions, are illustrated by curves 24, 26 and 28 respectively in Figs. 7, 8 and 9. These show a considerable improvement by comparison with the improved prior art method A. The diagrams show the optimum conditions, expressed by equations (26) to (28). Even if these optimum conditions are departed from, such as to establish values for quantities D, E and F which are higher than those lying along curves 24, 26 and 28 in Figs. 7 to 9, a considerable improvement can still be obtained by comparison with the prior art examples discussed above. The embodiment of the present invention described above will be referred to as drive method C.

It can thus be understood from the above that utilizing the drive method according to the present invention not only enables a considerable improvement to be attained with regard to disadvantages (2) to (4) of the prior art as described above, but also provides an amelioration of disadvantage (1). An example of this will be described for the case of liquid crystal display elements being used. Liquid crystal display elements can be manufactured to operate with a value of Von which is in the range 2 to 1 OV. In the case of prior art example A, from conditions (1) and (2) above, since F t 1.5, it is necessary to use non-linear elements which have a threshold voltage Vth of 3 to 1 5V or more. Elements having such a high value of threshold voltage Vth include varistors, MIM diodes, etc. The manufacturing deviations in the characteristics of ZnO varistors, as given in prior art reference 2, are of the order of +5V. Thus, successful operation using such elements as varistors or MIM diodes is difficult.to attain, due to the large amount of deviation in the value of threshold voltage Vth. It is possible to obtain a high value of threshold voltage by connecting a large number of silicon diodes in series, and utilizing their forward conduction threshold voltage. This can provide non-linear elements which have a comparatively low amount of stray deviation in Vth, and prior art reference (1) described an example in which 40 PN diodes are connected in series. However it is almost impossible to form a large number of such elements in each picture element of a display panel, and in addition it would be difficult to attain a sufficiently high manufacturing yield using such a method. Since a high value of Vth is necessary with these prior art examples, it has not been possible to utilize display elements which have good control characteristics. With the present invention however, a value of Vth of the order of 0.6 to 0.7V provided by a single PN junction, is quite sufficient. For example, satisfactory display quality can be obtained using liquid crystal display elements if Von = 2V, and drive margin M = 1.5V approximately. As can be seen from Fig. 7, these conditions can be satisfied by drive method (C) of the present invention, with Vth = 0.35V, and Von = 0.7V.

Fig. 10 shows the configuration of a non-linear 7 resistor element 30, used in an embodiment of the present invention. This comprises a pair of silicon diodes 32 and 34, connected in parallel to one another with opposing polarities, in a ring 5 configuration.

Fig. 11 and 12 are plan and cross-sectional views respectively of this embodiment of the present invention, showing a portion of a display panel substantially corresponding to a single picture element. Numerals 44 and 46 each denote 75 a single amorphous silicon diode, 36 denotes a column electrode, numeral 41 denotes a connecting electrode, numeral 37 and 40 denote amorphous silicon structures, numeral 39 denotes a transparent connecting electrode, numeral 42 denotes a display element, numerals 60 and 68 denote upper and lower substrates respectively, numeral 64 denotes a liquid crystal layer, numeral 66 denotes a row electrode and numerals 54, 56 and 58 respectively denote p+, i (intrinsic), and n+ layers of amorphous silicon. Numeral 47 denotes a light source whose light is incident on the side of the display corresponding to column electrode 36.

The I-V characteristics of an amorphous silicon diode ring having the structure described above are shown in Fig. 13. Fig. 14 shows the distribution of Vth for a number of different non linear elements having the configuration of such an amorphous silicon diode ring. As shown, the values of Vth ior most of the elements fall within a range of 40 mv 3%. With the drive method according to the present invention, if the drive margin M = 1.2, then D = 1/6, so that the manufacturing deviation of Von between different elements will be +3/6%, i.e. +0.5%. As a result, extremely uniform display characteristics can be obtained. In addition, the value of peak-to-peak drive voltage required, Vp-p, is independent of the numers; of row electrodes and column electrodes N and M of the matrix, being approximately 4.3V, so that the display can easily be driven from a 5V power supply.

Fig. 15 is a block diagram of a matrix display device according to the present invention.

Numeral 70 denotes a display panel of the type illustrated in Fig. 12 and Fig. 13, numeral 72 denotes a row electrode drive circuit for applying row drive signals S1 to SN' comprising scanning signals of the form 0% shown in Fig. 6 to the display panel.

Numeral 76 denotes a column drive circuit for applying column drive signals comprising data signals of the form Y shown in Fig. 6 to the column electrodes D1 to D., numeral 74 denotes a controller circuit for supplying to the drive circuits display data signals 78, timing signals 82 and 84, and power supplies 80, 81 etc.

Fig. 16 shows an example of a row electrode drive circuit. Fig. 17 is the corresponding timing chart. Numeral 86 denotes a shift register circuit, numeral 86 denotes a group of latch circuits, numeral 90 denotes a group of AND gates, numeral 92 denotes a group of voltage selector gates for selecting a single potential from among potentials +Va, Vb, in accordance with the 130 GB 2 129 182 A 7 signals Hn, In, Jn and Kn, and for supplying the selected signal potential (having the waveform of signal 0% shown in Fig. 6), to the row electrodes.

Fig. 18 shows an example of a controller circuit for producing drive signals for an analog type of matrix display device according to the present invention, e.g. a television receiver. Numeral 102 denotes an antenna, numeral 104 denotes a tuner, numeral 106 a video amplifier, numeral 108 denotes a sync separator circuit, numeral 110 denotes a reference pulse generating circuit, and numeral 112 denotes a reference voltage generating circuit.

Fig. 19 shows an example of a column electrode drive circuit for an analog display type of matrix display device, operating on a line-at-a-time scanning system. Numeral 120 denotes a sampling pulse generating circuit and numerals 122 and 124 denote sample-and-hold circuits. In this example, as opposed to the example of Fig. 6, an analog display signal Y. varies in a continuous (i. e. non-stepwise) manner between -Vc and Vc, with the polarity of this signal being inverted at the start of successive frame intervals T1 and T2 by means of a polarity inverting circuit 126.

A large number of display elements, e.g. with 1000 or more rows and columns, can be provided in a matrix display device in accordance with the above embodiments of the present invention, so that the present invention is widely applicable to television receivers, computer terminals etc. The drive margin can be set to the order of 1.5, so that the display quality is significantly better than that of a prior art passive type of matrix display device, and is comparable to that of an active-element type of matrix display device utilizing 3- terminal elements (e.g. thin-film transistors). In addition, the present invention provides significantly greater tolerance against manufacturing deviations in the display element characteristics, by comparison with the prior art, and in addition enables nonlinear elements which have a low value of threshold voltage Vth such as amorphous silicon diodes to be utilized. Furthermore, a power supply providing 5V or less is sufficient to provide power to operate the display device, which is significantly less than the 10 to 30V power supply voltage that is required by prior art passive matrix or thin-film transistor active matrix displays.

Furthermore, the matrix elements of a matrix display utilizing the method of the present invention can be manufactured by a process which involves only from 3 to 5 layers, shaped by masking steps. Thus, the manufacture of such a display device will require less time than in the case of a matrix display device utilizing thin-film transistors, which requires from 4 to 7 layers. In addition, since an MOS interface is not utilized in the display elements of a display device according to the present invention, a high degree of stability can be attained.

As described above, a display device utilizing the drive method of the present invention possesses significant advantages by comparison 8 GB 2 129 182 A 8 with prior art types of display device, e.g. passive types of display device which utilize non-linear resistor elements or active types of display device which utilize transistors, and may very well become the principal type of high-density display to be used in the future.

In the embodiments described above, amorphous silicon diodes are used as the nonlinear resistor elements, however it is also possible to use devices such as Schottky barrier diodes of MIM diodes to obtain the respective advantages of these devices. In addition, rather than implementing each of the non-linear elements by single stages of diodes, it is equally possible to utilize a plurality of diode stages connected in a series-parallel arrangement for each of these elements. These non-linear elements can also be formed by a multi-layer or a planar configuration. The material for the diodes is not limited to a - Si:H, and it is equally possible to use a - Si:C, a - Si:N, a - Si:O, Cd, CdS, InSb, GaAs, InP, Se, Te, etc. In addition, if a suitable level of control of the characteristics can be attained, it is of course also possible to use varistors or other types of non linear elements. Furthermore, although liquid crystal is used for the display elements of the above embodiments, it is equally possible to use electrochromic, electro-luminescent, or other types of display element.

Fig. 21 shows a reference voltage setting circuit for automatically compensating for any changes occurring in the threshold voltage of the non-linear elements. The threshold voltage Vth of a reference non-linear element 128 shown in the diagram is compared with reference potentials (Va - VthO) and (Vb - VthO) (where VthO is some predetermined nominal value of threshold voltage), such as to automatically adjust the value of Va to become (Va + d'Vth) and adjust Vb to become (Vb + d'Vth), to adjust -Va to become (-Va - d'Vth), and to adjust -Vb to become (-Vb - d'Vth), where d'Vth is equal to Wth - VthO). If this is done, then the voltages which are applied to drive the display elements do not change in response to changes in the threshold voltage Vth resulting from operating temperature variations.

Although the method of the present invention has been described in the above with reference to specific embodiments, it should be noted that various changes and modifications to these embodiments may be envisaged, which fall within 11 the scope claimed for the invention, as set out in the appended claims. The above specification should therefore be interpreted in a descriptive and not in a limiting sense.

Claims

1. A method of driving a matrix display device formed of a plurality of row electrodes, a plurality of column electrodes and a plurality of matrix elements disposed at intersections of said row electrodes and column electrodes, each of said matrix elements comprising an electro-optical display element and a non-linear resistance element connected in series between one of said row electrodes and one of said column electrodes, said non-linear resistance element having a threshold voltage above which a significant increase in the resistance thereof occurs, said method comprising: applying row scanning signals successively to said row electrodes, said row scanning signals being applied periodically to corresponding ones of said row electrodes during successive scanning frame intervals, each of said row scanning signals being set to a first potential during a selection interval of fixed duration and timing within a frame interval and going to a second potential during a non-selection interval immediately thereafter and remaining fixed at said second potential during at least a major portion of the time which elapses until initiation of a succeeding selection interval during the succeeding frame interval, with the absolute value of said first potential being higher than the absolute value of said second potentiall and said first and second potentials having the same polarity; applying data signals varying in potential over a predetermined range to said column electrodes, with a synchronized relationship being established between said row scanning signals and said data signals such that a drive potential corresponding to a data value is applied across each of said matrix elements during a corresponding one of said selection intervals; the values of said first and second potentials of said row scanning signals and the potential range of said data signals being selected such that the absolute value of the difference between the drive potential established across a matrix element during a selection interval and the potential established across the display element of that matrix element during the immediately succeeding non-selection interval is always less than or equal to the threshold potential of said non-linear resistance elements.

2. A method according to claim 1, in which if the selection intervals and non-selection intervals of successive frame Intervals are sequentially numbered, each of said row scanning signals goes to said first potential in the even-numbered selection intervals, goes to said second potential in the even-numbered non-selection intervals, goes to a potential which is equal in absolute value to said first potential and of opposite polarity thereto in the odd- numbered selection intervals, and goes to a potential which is of equal absolute value to said second potential and of opposite polarity thereto during the odd-numbered non- selection intervals.

3. A method according to claim 2, in which designating said threshold voltage as Vth, said first potential as Va, said second potential as Vb, and the range of variation of said data signals as extending from a potential Vc to -Vc, the relationships between these potential satisfy the following conditions:

9 GB 2 129 182 A 9 (Va - Vb):5 Vth 2Vc:t- Vth

4. A method according to claim 2, in which if the maximum value of potential which is applied across each of said display elements is designated as Von, the minimum value thereof is designated as Voff, and the ration Von/Voff is designated as a drive margin M, then the following relationships between Va, Vb, Vc and Vth are substantially 10 satisfied:

Va < R3M - 10M - 1) 1. Vth/2 Vb:! I(M + 1)/M - l)). Vth/2 W:

5 V02 5. A method of driving a matrix display device according to claim 2, in which designating said first potential as Va and said second potential as Vb, the relationships between the amount of stray deviation AVth in the threshold potential Vth of said non-linear resistance elements and the potentials V1a and Vc substantially satisfy-the following conditions:

Va - Vb -- Rth - AVth) Vc = Wth -AVtW/2

6. A method of driving a matrix display device according to claim 2, and further comprising the steps of deriving a voltage which varies with temperature in accordance with variations in the value of said threshold voltage with temperature, producing first and second fixed potentials, comparing said first and second fixed potentials with said temperature- varying voltage, and controlling the levels of said first and second potentials of said row scanning signals in accordance with the results of comparisons with said first and second fixed potentials respectively, to thereby adjust the values of said first and second potentials such as to compensate the operation of said matrix display device against changes in said threshold voltage with temperature.

7. A method of driving a matrix display device substantially as hereinbefore described with reference to figures 6-21 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1984. Published by the Patent Office,. 25 Southampton Buildings, London. WC2A lAY, from which copies may be obtained.